Question

if the masses remain the same ,but the separation is decreased to one-half of the original distance . what happens to the gravitation force?

Answer 1

f = GMm/r^2
if you replace r by r/2, you have

GMm/(r/2)^2 = 4GMm/r^2 = 4f

so, the force increases 4-fold
If r changes by a factor of k, the force changes by a factor of 1/k^2

Answer 2

F =G•m1•m2/R²
the gravitational constant
G =6.67•10⁻¹¹ N•m²/kg²,
R1=r/2 => F1=4F